1. Field of the Invention
The present invention provides an inhibitor for .DELTA.5-desaturase which specifically inhibits the conversion of dihomo-.gamma.-linolenic acid to arachidonic acid. This inhibitor remarkably increases, in vivo, the amount of dihomo-.gamma.-linolenic acid in comparison with arachidonic acid.
2. Description of the Related Art
Various studies relating to the actions of essential fatty acids on an organism show that not only are there two metabolic pathways for essential fatty acids, which pathways strongly influence each other, but also in the same metabolic pathway there are various metabolites which act antagonistically, and therefore, to enhance an action it is necessary not only to administer a related metabolite but also to inhibit an antagonistic action against the above-mentioned action. In the case of dihomo-.gamma.-linolenic acid and a metabolite thereof, i.e., arachidonic acid, an eicosanoid derived from dihomo-.gamma.-linolenic acid and an eicosanoid derived from arachidonic acid antagonistically influence each other, and therefore, to enhance the effects of an administration of dihomo-.gamma.-linolenic acid, it is necessary to inhibit the conversion of dihomo-.gamma.-linolenic acid to arachidonic acid. At present, although a series of prostaglandin 1 derived from dihomo-.gamma.-linolenic acid is known to have an antithrombus activity, unless inhibiting the conversion of dihomo-.gamma.-linolenic acid to arachidonic acid, the desired expected effect provided by administering dihomo-.gamma.-linolenic acid is not obtained.
It is known that among lignan compounds, sesaminol, episesaminol, 2-(3,4-methylenedioxyphenyl) -6-(3-methoxy-4-hydroxyphenyl)-3,7-dioxabicyclo[3.3.0]-octane, 2,6-bis-(3-methoxy-4-hydroxyphenyl)-3,7 -dioxabicyclo[3.3.01octane and 2-(3,4-methylene -dioxyphenyl)-6-(3-methoxy-4-hydroxyphenoxy)-3,7-dioxabicyclo[3.3.01]octan e are comparable with or superior to sesaminol and .gamma.-tocopherol in the antioxidation activity thereof, and are being developed as antioxidants. Moreover, these lignan compounds are under study for possible application for inhibition of lipid peroxidation in vivo which is considered a cause of senility, oncogenesis and the like. However, among lignan compounds, anti-oxidation activity of sesamin, episesamin and sesamolin is not known.
Moreover, it is not known that the above-mentioned lignan compounds inhibit .DELTA..sup.5 -desaturase, which catalyzes the conversion of dihomo-.gamma.-linolenic acid to arachidonic acid.
In addition, it is not known that curcumin and piperonyl butoxide inhibit .DELTA..sup.5 - desaturase.